This invention relates to a multiplex communication arrangement which is of an N:1 redundancy configuration and in which a stand-by demultiplexer is used to selectively monitor N active multiplexers as a part of a monitoring circuit for the multiplexers. Such a multiplex communication arrangement is said in the art to be capable of carrying out self-monitoring or self-diagnosis and is reliably operable.
In the manner which will later be described more in detail, a conventional multiplex communication arrangement of the above-described type comprises (N+1) multiplexers connected to a plurality of transmission channels or routes, respectively. Each transmission channel corresponds to a respective multiplexer. The arrangement further comprises (N+1) demultiplexers, each connected to a selector or switching device which is connected in turn to one of a plurality of reception channels that corresponds to the selector and consequently to the demultiplexer under consideration.
N multiplexers of the (N+1) multiplexers are used at any time as active multiplexers. Each active multiplexer multiplexes a plurality of multiplexer input signals into a single multiplexer output signal for transmission to one of the transmission channels that corresponds to the multiplexer in question and is used as an active transmission channel. The one remaining multiplexer is used as a stand-by multiplexer and is connected to one of the transmission channels that corresponds to the stand-by multiplexer and is used as a stand-by transmission channel.
N demultiplexers are used at any time as active demultiplexers They are connected to N reception channels, respectively, which are used as active reception channels. The one remaining demultiplexer is used as a stand-by demultiplexer and is connected to the one remaining reception channel that is used as a stand-by reception channel. The N selectors associated with the active demultiplexers connect those demultiplexers to the corresponding active reception channels. The remaining selector connects the stand-by demultiplexer, not to the stand-by reception channel, but to one of the active transmission channels that is selected as a selected transmission channel and is supplied with the multiplexer output signal as a selected multiplexer output signal. Each active demultiplexer demultiplexes a demultiplexer input signal received through its corresponding reception channel and its associated selector to generate a plurality of demultiplexer output signals. Similarly, the stand-by demultiplexer demultiplexes the selected multiplexer output signal into a plurality of demultiplexer output signals.
A comparator carries out bit by bit comparison of the demultiplexer output signals of the stand-by demultiplexer with the multiplexer input signals supplied to one of the multiplexers that is connected to the selected transmission channel. In this manner, the combination of the stand-by demultiplexer and the comparator serves as a monitoring circuit for selectively monitoring the active multiplexers. It is to be noted, as described above, that the stand-by reception channel is not connected to the stand-by demultiplexer. The stand-by demultiplexer is therefore incapable of receiving a signal which would otherwise be supplied thereto through the stand-by reception channel. As a result, multiplex communication arrangement is incapable of detecting errors present in the signal on the stand-by reception channel.